Method of Regenerating Filter Fabric and Regenerated Filter Fabric

ABSTRACT

A method of regenerating a filter fabric, comprising at least fibrillating a spent filter fabric and converting the fibers resulting from the fibrillation operation into a nonwoven fabric. In this method, a dust removing operation of removing any dust adhering to the fibers resulting from the fibrillation operation may be performed prior to the above mentioned formation of the nonwoven fabric. Further, it is preferred from the viewpoint of efficient regeneration that the fibrillation operation be performed by passage through an auto fibrillation machine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for regenerating a used filter fabricand a regenerated filter fabric obtained by regenerating a used filterfabric.

2. Description of the Related Art

Many of conventional filter fabrics have practically been disposed afteruse because of time and money of the recycling work. However, filterfabrics sometimes bear harmful components such as dioxin in form of dustthrough their utilization. Therefore, an incineration disposal or alandfill disposal costs time and money and is not environment-friendlyin terms of global environmental preservation. In such a situation, ithas strongly been desired to develop efficient recycling and reuse of aused filter fabric.

As a conventional recycling technique of a filter fabric, there is aregeneration method of washing out adhering dust with water such asspraying flowing water on the surface of a used filter fabric or awashing chemical agent (see e.g. reference to Japanese Patent Laid-Open(JP-A) No. 2003-103128).

However, such a method of washing with water only separates a portion ofdust adhering to the surface layer of component fibers resulting in alot of dust adhering to the inside being remained. Therefore, a filterfabric regenerated by water washing has a much higher pressure loss thana new one. For example, according to the test results shown in Table 1,the initial pressure loss is 70 Pa for a new one while it is 106 Pa forthe regenerated one. Like this, it has been impossible to obtain aninitial pressure loss as low as that of a new one after regeneration.

Further, attributed to the remaining of the dust in the inside, dusttends to be accumulated in the inside. Therefore, the filter fabricregenerated by water washing shows very quick increase of the pressureloss and is more likely to cause clogging. For example, according to thetest results shown in Table 1, although backwashing is carried outfrequently to fix the clogging, the pressure loss after 8 hours use is302 Pa while it is 122 Pa for a new one. As described, afterregeneration, it has been impossible to obtain a lifetime as long asthat of a new one.

Further, since the clogging is easily occurred, frequent backwashing forshaking off the dust by blowing compressed air in the inversed directionto the air filtration direction is required in order to lower thepressure loss. However, at the time of backwashing, since the twistingof fibers is weakened for a moment, the once collected dust (in theinside of the filter fabric) flows out toward the outlet due to the flowof dust-containing air. For example, it is found from the test resultsshown in Table 1 that the accumulative outlet dust concentration is 2.15mg/m³ after 8 hours use, while it is 1.173 mg/m³ for a new one. Asdescribed, if backwashing is carried out frequently, the outlet dustconcentration is increased and thus it has been impossible to achieve adust collection efficiency as high as that of a new one afterregeneration.

Further, since the twisting of the fibers is weakened due to not onlythe high water pressure brought to the surface layer of the filterfabric but also the frequent backwashing, the strength and elongation ofthe regenerated filter fabric is considerably deteriorated as comparedwith a new one.

There have been regenerable filter fabrics coated with a thermofusiblebinder resin or a solvent-soluble binder resin as another regenerationtechnique of a filter fabric (see e.g. reference to JP-A Nos. 9-253432and 2001-336054). In this regeneration technique, by a heat-treatment ofa used fiber fabric or an immersion treatment of a used fiber fabric ina solvent, dust can be easily and highly efficiently separated from thefilter fabric with melting the binder resin. Accordingly, this techniqueis to inhibit the increase of the pressure loss and the time to the samelevel as those of a new filter fabric and at the same time secure thefiltering efficiency and the strength of the regenerated filter fabricby preventing the damages on component fibers.

However, since the regeneration method involves heat melting or chemicalreaction, the filter fabric cannot be used at a high temperature or inchemically severe environments and thus only limited application ispossible.

Further, since a costly special binder resin is applied by specialcoating process and separated by special separation process at the timeof regeneration, the production cost is high and the filter fabric isnot economical. In addition, even if dust can be separated from fibersat the time of regenerating the fibers, it is still difficult toseparate the dust from the binder resin and regenerate the binder resinitself. Therefore, the regenerated filter fabric is inferior for thepractical use in terms of the cost.

In view of the above-mentioned state of the art, it is an object of theinvention to provide an economical and practically applicableregeneration method for a used filter fabric by which the pressure lossand the filtering efficiency are kept as good as those of a new filterfabric even after regeneration and by which a regenerated filter fabricis usable even at a high temperature or in chemically severeenvironments without limiting its application and it is also an objectof the present invention to provide an economical regenerated filterfabric by this method.

Patent Document 1: Japanese Patent Laid-Open No. 2003-103128 PatentDocument 2: Japanese Patent Laid-Open No. 9-253432 Patent Document 3:Japanese Patent Laid-Open No. 2001-336054 SUMMARY OF THE INVENTION

To solve the above-mentioned problems, the invention employs thefollowing means (1) to (12).

(1) A regeneration method of a filter fabric of the invention involvesat least fibrillation treatment for fibrillating a used filter fabricand nonwoven treatment for producing a nonwoven fabric from the fibersobtained by the fibrillation treatment.

The fibrillation treatment of the invention here means treatment forfibrillating a used filter fabric to individual single fiber elements.Also, the nonwoven treatment of the invention means treatment forproducing a nonwoven fabric in a desired shape made of mainly thefibrillated fibers held together by interlocking or fixing and bonding.

The above-mentioned regeneration method can reliably separate the dustadhering between the fibers, regardless of whether the dust adheres tothe surface or inside of the component fibers of the pre-regeneratedfilter fabric, since the regeneration is conducted by single fiber basisbecause of the fibrillation.

Consequently, the dust adhering to the inside of the component fibers,which cannot be separated by the above-mentioned water washing method,can be separated, so that the increase of the pressure loss and the timeand filtering efficiency can be kept approximately same as those of anew filter fabric even after regeneration. Further, twisting of thecomponent fibers is not weakened unlike the case of water washing andthe strength almost same as that of a new filter fabric can be secured.

Further, the nonwoven treatment strengthens the twisting of the fibersand as compared with the case of the above-mentioned water washingmethod, strength approximately same as that of a new filter fabric canbe obtained.

Since the regeneration method by the fibrillation treatment and thenonwoven treatment of the fibrillated fibers can be carried out withoutusing a thermally fusible or chemically reactive resin such as a binderresin, the filter fabric obtained by this method can be used at a hightemperature or in chemically severe environments and its application isnot limited unlike a filter fabric using the above-mentioned binderresin.

Further, since neither the above-mentioned costly binder resin is usednor the above-mentioned special coating process is needed, as comparedwith a filter fabric using the binder resin, the regeneration method ofthe present invention is economical and highly practically applicable.

(2) Alternatively, the regeneration method of a filter fabric of theinvention may involve powder dust separation treatment for separatingthe powder dust adhering to the fibers obtained by the fibrillationtreatment before the nonwoven treatment. That is, the regenerationmethod of a filter fabric may involve at least fibrillation treatmentfor fibrillating a used filter fabric, powder dust separation treatmentfor separating the powder dust adhering to the fibrillated fibers, andnonwoven treatment for producing a nonwoven fabric from the fibersobtained after the powder dust separation treatment.

Accordingly, more dust can be separated by carrying out the powder dustseparation treatment after the fibrillation to give an excellent airflowproperty and filtering efficiency.

Further, because of the nonwoven treatment, the twisting of the fibersis further strengthened and therefore, the strength is closer to that ofa new filter fabric as compared with the case of the above-mentionedwater washing method.

(3) In the above-mentioned regeneration method of a filter fabric of theinvention, the filter fabric is preferably fibrillated by an automaticfibrillation apparatus in the fibrillation treatment in terms ofefficient regeneration.

Accordingly, dust can easily be separated by the mechanical automaticfibrillation and consequently it makes the regeneration easy andeconomical.

(4) In the above-mentioned regeneration method of a filter fabric of theinvention, the used filter fabric is preferably a filter fabric used ina manner that adhesion of dioxin to the filter fabric is prevented byadding a chemical agent capable of decomposing both dioxin and dioxinorigin substances.

Herein, in the invention, dioxin origin substances mean dioxinprecursors such as chlorophenol, chlorobenzene, and the like.

Accordingly, the added chemical agent decomposes dioxin and dioxinorigin substances contained in dust-containing air during the use of thefilter fabric not becoming the used filter fabric, so that the dioxinconcentration itself is lowered. Consequently, the absolute number ofdioxin in the dust to be brought into contact with the filter fabric issuppressed and adhesion of dioxin to the filter fabric is inhibited. Insuch a manner, a filter fabric in which the dioxin adhesion to thefibers is inhibited is fibrillated as a used filter fabric, so that aregenerated filter fabric scarcely bearing dioxin can be obtained.

Accordingly, even a used filter fabric used in dioxin-containingatmosphere, which has been difficult to be regenerated conventionally,can be used as a raw material for regeneration. Consequently, theregeneration method can considerably save the time and money requiredfor the disposition procedure of the filter fabric bearing dioxin andthus can be economical and highly practically applicable.

(5) In the above-mentioned regeneration method of a filter fabric, theused filter fabric is preferable to be mainly made up of PTFE fibers.

Accordingly, it is enabled to obtain a regenerated filter fabricexcellent in the strength and filtering efficiency and also excellent inchemical resistance and heat resistance.

(6) Alternatively, in the regeneration method of the filter fabric, theused filter fabric is preferable to contain at least PTFE fibers andinorganic fibers.

Accordingly, the regenerated filter fabric is to contain fibrillatedinorganic fibers and thus the filtering efficiency of the regeneratedfilter fabric will be improved. Further, the time and money forseparating the inorganic fibers prior to the fibrillation treatment canbe saved and the regenerated filter fabric containing inorganic fiberscan efficiently be obtained.

(7) The regenerated filter fabric of the invention is characterized byincluding at least a dust collection layer mainly made up of thefibrillated fibers obtained by fibrillating the used filter fabric.(8) Also, the regenerated filter fabric may include a base cloth towhich the dust collection layer is fixed. That is, the regeneratedfilter fabric may include at least the dust collection layer formed byfibrillating the used filter fabric and the base cloth to which the dustcollection layer is fixed.

Accordingly, the filter fabric becomes stronger because of the basecloth and the twisting strength of the component fibers can be kept ashigh as that of a new filter fabric even if the filter fabric isbackwashed during its use.

(9) Further, the above-mentioned regenerated filter fabric may includethe dust collection layer which is made up of the fibrillated fibersmixed with auxiliary fibers.

That is, the regenerated filter fabric may include at least the dustcollection layer formed by mixing the fibers obtained by fibrillating aused filter fabric with auxiliary fibers, or the regenerated filterfabric may include at least the dust collection layer formed by mixingthe fibers obtained by fibrillating a used filter fabric with auxiliaryfibers and the base cloth for fixing the dust collection layer.

Accordingly, addition of the auxiliary fibers makes it possible to givethe regenerated filter fabric with high strength and elongation.

(10) With respect to the above-mentioned regenerated filter fabric, thedust collection layer may be formed by the nonwoven fabric produced fromthe fibers which make up itself (the dust collection layer) by nonwoventreatment.

That is, the dust collection layer may be formed by a nonwoven fabricproduced from the fibers obtained by fibrillating the used filterfabric, or the dust collection layer may be formed by a nonwoven fabricproduced from the mixed fibers of the fibers obtained by fibrillatingthe used filter fabric and the auxiliary fibers.

(11) With respect to the above-mentioned regenerated filter fabric, theused filter fabric is preferable to be mainly made up of PTFE fibers.(12) Alternatively, with respect to the above-mentioned regeneratedfilter fabric, the used filter fabric is preferable to contain at leastPTFE fibers and inorganic fibers.

It is made possible to provide an economical and practically applicableregeneration method for a used filter fabric by which the pressure lossand the filtering efficiency are kept as good as those of a new filterfabric even after regeneration and by which a regenerated filter usableeven at a high temperature or in chemically severe environments withoutlimiting its application and also provide a regenerated filter fabricobtained by this method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing an embodiment of a regeneration method ofa filter fabric of the present invention;

FIG. 2 is an electron microscopic photograph of a regenerated filterfabric according to an embodiment of the present invention; and

FIG. 3 is an electron microscopic photograph of a new filter fabric.

BEST MODE OF THE EMBODIMENTS OF THE INVENTION

Hereinafter, the constitution of the invention will be described indetail with reference to drawings and photographs for substitutingdrawings as an embodiment. FIG. 1 is a flow chart of a regenerationmethod of an embodiment of the invention and FIG. 2 is an electronmicroscopic photograph magnified at a magnification of 1000 timesshowing the fiber state fibrillated by the fibrillation treatment of theinvention. FIG. 3 is an electron microscopic photograph magnified at amagnification of 1000 times showing the fiber which is not subjected tothe fibrillation treatment for comparison with that shown in FIG. 2.

A filter fabric or a regenerated filter fabric used in this invention isa filter fabric to be employed for collecting powder. Particularly inthe embodiments described below, the filter fabric is fixed in a filterdust collection apparatus for filtering and collecting dust of anincinerator flue gas discharged out of an incinerator in incinerationfacilities and used for filtering and collecting dust in form of apowder containing harmful dust such as dioxin and heavy metals at a hightemperature, that is 150° C. or higher, in ambient environments.

The harmful dust means substances harmful in terms of environmentpreservation and health hygiene among the dust filtered and collected aspowder dust and for example, substances regulated and limited in thedischarge amount to the environments and the allowable intake in humanbody by official organizations and required to undergo scatteringprevention treatment at the time of disposition.

Particularly, dioxin is generally evaluated as highly toxic substance inthe harmful dust and it is not only regulated according to the ambientenvironmental quality standard but also its pollution monitoring andremoval methods are specified. Conventionally, a filter fabric used indioxin-polluted environments has been entirely subjected to landfilldisposal since its efficient recycling has been difficult. On thecontrary, if the practically applicable regeneration method of a filterfabric of the invention is employed for regeneration and reuse of afilter fabric which is used for collecting dioxin-containing dust, notonly it is environmental-friendly in global environments but also itresults in prevention of harmful substance accumulation in human bodyand saving of treatment cost and labor.

In this connection, mercury, cadmium, lead and the like exemplified asheavy metals contained in the harmful dust are also regarded as harmfulsubstances whose accumulation in human body is a serious issue relevantto the treatment method and environmental preservation and if thepractically applicable regeneration method of a filter fabric of theinvention is employed for regeneration and reuse of a filter fabricbearing these heavy metals, it is environmental-friendly in globalenvironments and results in prevention of harmful substance accumulationin human body.

A filter fabric or a regenerated filter fabric of this embodimentincludes at least a dust collection layer containing PTFE fibers as amain component. Since PTFE fibers are excellent in chemical resistance,heat resistance, electric charge retention property, and strength, theyare suitable for a filtration and dust collection layer. On the otherhand, since PTFE fibers have the same problem of disposition as dioxinthat when they are incinerated, harmful gases including fluorinecompounds, e.g. hydrofluoric acid and fluorohydrocarbons are evolved andthus it is especially desired to regenerate and reuse the PTFE fibers.

The filter fabric having the dust collection layer containing the PTFEfibers can be used as a filter fabric for a high temperature of 150° C.or higher and accordingly it is made possible to use the filter fabricfor high temperature dust collection, unlike a conventional filterfabric which is coated with a thermally fusible binder resin and thusimpossible to be used for it.

The fibers for the dust collection layer may be formed from glassfibers, PPS, polyimide, meta-aramid besides the PTFE fibers or theirmixtures with the PTFE fibers. Particularly, the fibers of theregenerated dust collection layer are preferable to consist ofregenerated fibers as a main component and one or more kinds ofauxiliary fibers for assisting the functions of the filter fabric(strength, elongation, or filtering efficiency) mixed with theregenerated fibers.

The auxiliary fibers are preferable to be new (not used) fibers andspecifically, PTFE fibers suitable for a regenerated filter fabric orinorganic fibers such as silica, alumina, and glass fibers arepreferably used. Further, the auxiliary fibers are preferable to be longor thin as compared with other component fibers. In the regenerationprocess of a used filter fabric, the auxiliary fibers are added in “Stepof mixing auxiliary fibers” described later.

(Example of Regeneration Method)

As shown in FIG. 1, a regeneration method of a filter fabric of thisembodiment involves steps of (1) chemical agent addition treatment foradding a chemical agent during steady operation, startup (startingoperation), or shutdown (stopping operation) of an incinerator in orderto remove harmful dust components and prevent adhesion and formation ofthem; (2) water washing treatment for washing and drying the used filterfabric from which metals or the like are separated after being removedfrom a dust collecting apparatus; (3) fibrillation treatment forfibrillating the used filter fabric into each individual fibers; (4)powder dust separation treatment for separating powder dust adhering tothe fibrillated fibers; (5) nonwoven treatment for producing a nonwovenfabric from the fibrillated fibers subjected to the powder dustseparation treatment; (6) punching treatment for fixing the fibersformed into the nonwoven fabric to a base cloth by a needle punch; and(7) finishing treatment for preventing the fibers from dropping off byreinforcing and finishing the surface of the nonwoven fabric subjectedto the punching treatment. Herein after the respective treatment stepswill be described respectively.

(1 Chemical Agent Addition Treatment)

The chemical agent addition treatment is treatment for adding a chemicalagent to a filter fabric during operation of an incinerator or a dustcollecting apparatus, that is, while the filter fabric is being used.Specifically, the treatment consists of steady operation treatment forspraying the chemical agent for preventing formation of harmful dust andremoving the harmful dust during the steady operation of theincinerator, and startup and shutdown operation treatment for spraying aharmful dust decomposition and removal agent at the startup and shutdowntime of the incinerator. Accordingly, the filter fabric can be usedwhile the absolute number of harmful dust particles in dust-containingair being decreased and adhesion of the harmful dust to the filterfabric being inhibited.

In this embodiment, the above-mentioned chemical agent is fordecomposing both dioxin and dioxin origin substances and in the usedfilter fabric subjected to the chemical agent addition treatment, theadhesion of harmful dust is inhibited: for example, in the case ofdioxin, its adhesion is inhibited to the level of 3 ng (nano-gram)-TEQ/gor less.

Additionally, the chemical agent addition treatment is treatmentrequired in the case where harmful dust containing dioxin and dioxinorigin substances is generated, and therefore if no harmful dust isgenerated, this treatment is not required.

The steady operation treatment is treatment for spraying a harmful dustformation prevention agent by a spray periodically to an area from acooling tower to a dust collecting apparatus. Because of this treatment,the formation of harmful dust which is formed slightly and graduallyduring the operation of the incinerator is inhibited and the harmfuldust is adsorbed and removed in the dust collection apparatus.

In the case where the harmful dust is gaseous and solid dioxin, theharmful dust formation prevention agent contains activated carbon andslaked lime for adsorbing gaseous or solid dioxin as main components andfor example, US LIME CD (trade name), manufactured by UEDA LIME CO.,LTD. may be used. Also, TAMAKARUKU (trade name) manufactured by YAKUSENSEKKAI Co., Ltd. is usable. When the harmful dust formation preventionagent is sprayed, the agent prevents adhesion of solid dioxin, which iscontained in harmful dust, to the filter fabric by forming a harmfuldust removal layer with a thickness of several μm on the filter fabricin the dust collecting apparatus.

The startup and shutdown operation treatment is treatment for spraying aharmful dust decomposition and removal agent by a spray to an area fromthe cooling tower to a flue and the dust collecting apparatus at thestartup time and shutdown time of the incinerator. Accordingly, aharmful dust decomposition and removal layer is formed in the entirebody of the main path of dust-containing air to decompose the harmfuldust and its origin substances. Specifically, by spraying about 300mg/Nm³ of the agent, high concentration dioxin and dioxin originsubstance formed in the flue and the dust collecting apparatus aredecomposed at the startup time and shutdown time of the incinerator ofwhich atmosphere is 300° C. or lower.

Herein, the startup time and shutdown time of the incinerator means apart of operating time of the incinerator and the dust collectingapparatus. Specifically, this means the time for inspection of apparatusgenerally conducted once every about 3 months in the case of relativelylarge scale incineration facilities and also the time when theincinerator and the dust collecting apparatus are stopped at every about7 to 10 days interval in the case of relatively small incinerationfacilities.

The dioxin origin substances mean dioxin precursors such as chlorophenoland chlorobenzene. The dioxin precursors are substances causingsecondary products of dioxin in the outside of the incinerator.

The harmful dust decomposition removal agent to be used may be ASHNITEMULTI A (trade name) manufactured by Kurita Water Industries Ltd. Theagent decomposes dioxin contained in the gaseous and solid harmful dustand also decomposes dioxin origin substances to prevent formation ofharmful dust. Accordingly, the agent can prevent increase of the dioxinin dust-containing air and simultaneously decreases the concentration ofdioxin and dioxin origin substances. Consequently, dioxin deposition andadhesion to the filter fabric can be prevented.

(2 Water Washing Treatment)

The water washing treatment is treatment for immersing a used filterfabric in flowing water so as to wash out easily separable dust afterthe used filter fabric is removed from the dust collecting apparatus andmetal or the like is separated from the filter fabric. It is preferableto add a surfactant to the flowing water for adsorbing and separatingdust chemically. Specifically, the filter is washed with a double-shellrotary drum type water washing apparatus or the like and dried.

The used filter fabric means a filter fabric which loses the function asa filter fabric if it remains fixed in the dust collecting apparatus dueto the continuous use of the filter fabric with fixing in the dustcollecting apparatus. Specifically, the used filter fabric means afilter fabric which has been used for filtering and collecting dust ofan incinerator flue gas while appropriately being back-washed withcompressed air and accordingly contains solid dust deposited even in theinside. Further, the used filter fabric means a filter fabric whoseairflow degree is lowered to 1 cc/cm²/sec or lower or whose pressureloss becomes 1800 Pa or higher during the operation and a clogging isoccurred at least partially or a filter fabric whose fibers are visuallyfound broken or decaying in the surface or the inside and thus which hasa problem in the filtering efficiency. That the filter fabric has aproblem in the filtering efficiency means that the powder leakage occursat least partially and thus the dust concentration at the outlet isconsiderably decreased during operation and that at least a portion ofthe filter fabric rather much expanded due to a long time use issignificantly parted from the filter fabric attachment means such as ashape retaining metal (a retainer), or that the twisted fibers of thefilter fabric rather shrunk due to a long time use are loosened(untwisted) and torn out. A filter fabric becomes the used filter fabricafter continuous use for about 5 months to 5 years in the case of commonhigh temperature dust collection with a dust collecting apparatus andparticularly in the case of dust collection of an incinerator flue gasfrom an incinerator, it becomes the used filter fabric after using forabout 3 to 5 years.

The wet washing for such chemical separation has high washing efficiencyas compared with that of backwashing carried out by blowing compressedair while the filter fabric being fixed in the dust collectingapparatus. This treatment is carried out before the fibrillationtreatment described later, so that dust separation with high efficiencyin the fibrillation treatment can be achieved. However, since it isdifficult to apply sufficient water pressure to the portions other thanthe surface layer of the filter fabric, it is impossible to completelywash out dust or the like adhering to the component fibers in theinside.

(3 Fibrillation Treatment)

The fibrillation treatment is treatment for fibrillating the used filterfabric into each individual fibers in order to separate the dust cloggedamong the fibers in the inside of the component fibers andsimultaneously removing even the dust electrostatically attracted to theindividual fibers by applying physical pressure and impacts andvibrations at the time of fibrillation. Accordingly, a highly powerfulregenerated filter fabric can be obtained easily and economically andpractical regeneration is made possible. In this embodiment, thefibrillation treatment is carried out by passing the used filter fabricthrough an automatic fibrillating apparatus.

The automatic fibrillating apparatus means a fibrillating apparatus forautomatically carrying out fibrillation of fibers by motive power otherthan manual work and thus excludes fibrillation solely by manual.Specifically, feeding of the filter fabric into the fibrillatingapparatus prior to fibrillation and fibrillating the fed filter fabricare continuously carried out by motive power other than a manual work,or by a combination of a manual work and motive power other than themanual work. For example, the used filter fabric is repeatedly put intoa dry type automatic fibrillating apparatus such as combing rolls untila bundle of fibers is untwisted so that fibrillated individual fiberswith a fiber length of 10 to 50 mm, preferably 20 mm to 40 mm areobtained. Any kinds of rolls such as needle blade type rolls, garnetrolls, and others may be used for the combing rolls.

At the time of the fibrillation treatment, apiece of cloth as auxiliaryfibers which are added in the auxiliary fiber addition step describedlater may be added to simultaneously carry out the fibrillationtreatment and the auxiliary fiber addition step.

(4 Powder Dust Separation Treatment)

The powder dust separation treatment is for separating dust adhering tothe individual fibers after the fibrillation using a conventionallyknown powder dust separation apparatus. As a conventionally known powderdust separation apparatus, there are Micron Separator (trademark) (MS-1)manufactured by HOSOKAWA MICRON Corporation; WOOL CLEANER manufacturedby OSAKA KIKO Co., Ltd.; and Binder Remover manufactured by IKEGAMIKIKAI Co., Ltd. and in addition to dry type separation apparatuses suchas punching metal separation and airflow separation, wet type separationapparatuses such as the water washing apparatus to be used for theabove-mentioned water washing treatment can be employed. Since thepowder dust separation is carried out after the fibrillation, the powderdust adhering to the individual fiber elements can be separated with ahigh efficiency. Accordingly, fine dust which is accumulated even in theinside of the filter fabric while being used and which cannot be removedby a conventional regeneration method such as backwashing or waterwashing can be separated. As another method, the powder dust separationtreatment may be carried out by water washing.

(5 Nonwoven Treatment)

The nonwoven treatment involves an auxiliary fiber addition step foradding auxiliary fibers to a large number of fibrillated fibers and alap-forming step for forming the individual fibers into a dustcollection layer of the regenerated filter fabric.

The auxiliary fiber addition step is a step for adding fibers which arelonger than the fibrillated individual fibers so as to strengthen thetwisting of one fiber to another fiber making up the nonwoven fabric andtherefore increase the strength and elongation of the regenerated dustcollection layer. This step is optionally added depending on theintended purposes of the regenerated filter fabric. Specifically,auxiliary fibers with a fiber length of 50 to 70 mm and a diameter of 5to 20 μm are added evenly at a ratio of 20 to 70% by weight, preferably30 to 60% by weight.

The material of the auxiliary fibers to be used in the embodiment arePTFE fibers same as those used for pre-regeneration dust collectionlayer and new fibers which have not been used for filter fabric. Besidesthem, the auxiliary fibers may include fibers of other materialsdifferent from that of the dust collection layer as long as they arewithin the scope of the use purpose of the auxiliary fibers and forexample, inorganic fibers (silica, alumina, glass fibers etc.) with asmaller fiber diameter than that of the PTFE fibers may be used. Theauxiliary fiber addition step strengthens the twisting of the fibers ofthe regenerated dust collection layer. Further, by addition of the glassfibers, the electrostatic effect is increased to improve the dustcollecting efficiency of the regenerated dust collection layer.

The fineness of the auxiliary fibers is in a range of 1 to 15 dtex,preferably 3 to 10 dtex. This is because the auxiliary fibers with afineness lower than 1 dtex are scarcely available and the auxiliaryfibers with a fineness of 15 dtex or higher increase the pressure loss.Addition of the auxiliary fibers with a small fiber diameter decreasesthe pressure loss because this makes the average fiber diameter of theentire dust collection layer to smaller.

The lap-formation step is a step for forming the fibrillated fabrics,which is mixed with the auxiliary fibers if necessary, into a desiredshape to make the dust collection layer of the regenerated filterfabric. The desired form means such shapes which are workable as thedust collection layer when being placed, for example, a plate-like, aweb-like, and a sheet-like shapes. Conventional forming method such as acard forming system by compressing the fibers in sheet-like form bycompression rolls, an air-layer system for forming a sheet by suckingair, as well as conventional forming method such as paper making systemcan be employed. An oil agent or the like may be added to suppressstatic electricity and friction at the time of the formation.

(6 Punching Treatment)

The punching treatment is treatment for fixing the dust collection layermade up of the formed fiber group with a base cloth by needle punching.The base cloth is for increasing the strength and elongation of the dustcollection layer by being placed along the dust collection layer.Alternatively, the punching treatment is treatment for needle punchingonly the dust collection layer made up of the formed fiber group withoutattaching the base cloth or the like if appropriate. The needle punchingstrengthens the twisting of one fiber to another fiber making up thefiber group. In the case where the punching treatment is carried outwith attaching the base cloth, the strength and the elongation areremarkably improved.

The base cloth is preferable to be made of PTFE, the same material asthat of the dust collection layer. If it is made of PTFE, the filterfabric to be obtained is provided with excellent heat resistance,chemical resistance, and high purity even after regeneration. If adifferent material or a material mixed with a different material isused, the filter fabric can be economical while having a neededstrength. The material is preferable to have a strength of 100 N/cmwidth or higher and an elongation of 40% or lower.

(7 Finishing Treatment)

The finishing treatment is treatment for fixing the shape of theregenerated filter fabric consisting of the nonwoven fabric and may beoptionally carried out based on the necessity. Specifically, thetreatment includes resin finishing step for applying resin on thesurface of the regenerated filter fabric and heat treatment step inwhich the regenerated filter fabric is treated with heat.

The resin processing step is an optional step of preventing theindividual fibers from dropping off the regenerated dust collectionlayer and becoming dust by applying resin on the surface of the formeddust collection layer. The application of resin may be conducted byconventional means such as dipping in a liquid phase resin, spraycoating of the resin, or coating.

The heat treatment step is a step for stabilizing the shape of theregenerated filter fabric by heat treatment at 200 to 330° C. and thisis an optional step carried out depending on the intended use such ashigh temperature application. Accordingly, breakage of fibers can beprevented even in the case that the regenerated filter fabric is used ina high temperature of 150° C. or more.

(Specification of Obtained Product)

Hereinafter, a regenerated filter fabric of the present inventionobtained by the above-mentioned regenerating method is specified. Theregenerated filter fabric of the present invention includes at least adust collection layer made up of the fibrillated fibers obtained byfibrillating the used filter fabric. Also, the regenerated filter fabricmay include at least the dust collection layer made up of thefibrillated fibers obtained by fibrillating the used filter fabric and abase cloth on which the dust collection layer is fixed.

The used filter fabric contains at least PTFE fibers. The PTFE fibersare preferable to be a main component of the used filter fabric.Further, the used filter fabric is preferable to contain at leastinorganic fibers in addition to the PTFE fibers.

The dust collection layer is preferable to be made up of the nonwovenfabric produced from the fibers which makes up the dust collectionlayer. The fibers making up the dust collection layer itself containsmainly the fibrillated fibers obtained by fibrillating the used filterfabric. The fibers making up the dust collection layer may containauxiliary fibers added to the fibrillated fibers.

The base cloth is fixed to the dust collection layer if necessary toreliably provide the shape retention, the strength and the elongation ofthe dust collection layer. The base cloth is not essential if the dustcollection layer is given the needed strength by adding the auxiliaryfibers to the dust collection layer or the nonwoven treatment of thefibers making up the dust collection layer.

That is, the regenerated filter fabric provided with a sufficiently highstrength may include, for example, the following two kinds of filterfabrics: the regenerated filter fabric including the dust collectionlayer made up of a nonwoven fabric produced from the mixed fibers of thefibers obtained by fibrillating the used filter fabric and the auxiliaryfibers, and the regenerated filter fabric made up of a nonwoven fabricproduced from the fibers obtained by fibrillating the used filterfabric.

Further, the filter fabric provided with a desirable strength may be,for example, a regenerated filter fabric including the dust collectionlayer formed by using fibers obtained by fibrillating a used filterfabric and mixed with the auxiliary fibers and the base cloth for fixingthe dust collection layer.

Since the regenerated filter fabric of the invention is oncefibrillated, the fibers are fibrillated approximately evenly not only inthe surface layer of the dust collection layer but also its entire areato the thickness direction and therefore, a relatively thick fibrillatedlayer is formed.

Herein, the approximately even fibrillation means that 10 or lessbranched fibers are found existing per each pre-branched fiber trunk byeye observation, as shown in FIG. 2.

FIG. 2 is an electron microscopic photograph with a magnification of1000 times showing the fibers fibrillated by the fibrillation treatmentin the regeneration method of the invention. As a comparative reference,FIG. 3 is an electron microscopic photograph with a magnification of1000 times showing the fibers which are not subjected to thefibrillation treatment and thus not fibrillated.

The regenerated filter fabric of the invention is obtained byregenerating a filter fabric bearing dust owing to its use and dustslightly remains even by the regenerating method of the presentinvention. Specifically, in the dust collection layer of the regeneratedfilter fabric, dust in a concentration of about 1 g/m or lower, atlowest several mg/m², remains. Even if dust remains, as long as theinitial airflow volume of the regenerated filter fabric is same as thatof a new filter fabric, there is no problem for practical use. Further,even though the dust tends to be easily accumulated inside of theregenerated filer fabric during long use and the airflow volume isslightly increased owing to the remaining dust in the initial period, aslong as the initial airflow volume of the regenerated filter fabric issame as that of a new filter fabric, there is no problem for practicaluse. As shown in test results in Table 1, 135 Pa after 8 hour use is asatisfactory value for practical use.

With respect to the regenerated filter fabric of the invention, thefibers obtained by fibrillation have a fiber length of 20 to 40 mm andat longest 50 mm. This is a mechanical constraint to pass the fibersthrough an automatic fibrillating apparatus.

The density (METSUKE) of the filter fabric (METSUKE of the entire filterfabric including the base cloth and the dust collection layer) is about300 to 1000 g/m² (it is 400 g/m² or higher particularly for the filterfabric having the base cloth) and preferably 600 to 800 g/m².

With the regenerated filter fabric of this embodiment, the fibers areapproximately evenly fibrillated as shown in FIG. 2 by mechanicalfibrillation with an automatic fibrillating apparatus. The fibrillatedfibers are twisted to form an on woven fabric, so that a dust collectionefficiency can be as high as desired even if the density is low, about400 g/m². Accordingly, many regenerated fibers can be obtained from asmall amount of original fibers and the regenerated filter fabric isremarkably economical owing to the cost down of the raw material.

On the other hand, if the density of the dust collection layer is about500 g/m² or higher, more preferably 700 g/m² or higher, regeneratedfibers with a high density can be obtained from the evenly fibrillatedand highly dense fibers and therefore it is made possible to collectdust with a very small particle size, which has been impossible to becollected conventionally. Or, even in the case the thickness of the dustcollection layer is relatively thin, the pressure loss can be suppressedand also high dust collection efficiency can be achieved. Consequently,the regenerated filter fabric is economical.

Further, the fibrillated portions of the fibrillated fiber are extremelythin as compared with the main body of the fibrillated fiber. Therefore,the pressure loss in the fibrillated portions becomes insignificantwithin a measurement error and the dust collection efficiency isincreased as compared with that of a dust collection layer formed byonly non-fibrillated fibers.

The regenerated filter fabric of this embodiment contains fibersapproximately evenly fibrillated not only in the surface layer of thedust collection layer but also in its entire area to the thicknessdirection, so that no boundary layer is formed in the front and backfibrillated fiber layers and thus decrease of the dust collectionefficiency owing to inertia of air passing through different layersbetween the front and rear fibrillated fiber layers is not caused.Accordingly, the regenerated filter fabric can collect dust reliably andhave an excellent dust collecting efficiency.

The invention has been described with reference to specificconstitutions, apparatuses, and methods, and the invention is notlimited by the above-mentioned embodiments. For example, chemical agentaddition treatment, water washing treatment, powder dust separationtreatment, punching treatment, and the finishing treatment in theabove-mentioned embodiments may properly be selected depending on theintended use of the filter fabric and included in the respectivetreatment steps of the regeneration method if needed as long as theregeneration method involves at least fibrillation treatment (preferablyfibrillation treatment and nonwoven treatment). Also, similarly, othertreatments may be involved depending on the intended use of theregenerated filter fabric. Various modifications and specific processcombinations may occur in the art without departing from the true spiritand scope of the invention.

(Comparative Test)

The following comparative tests for Example 1 of the invention werecarried out. The products for comparison were a new filter fabric and afilter fabric obtained by only water washing treatment in theregeneration method of Example 1.

Example 1

As Example 1 of the invention to be used for the comparative tests wasemployed a filter fabric, BF-800 manufactured by FUJI Corporation,having a dust collection layer and a base cloth both made of PTFE fibersand being used for a TQPJ type filtering dust collection apparatusmanufactured by HOSOKAWA MICRON Corporation for 6 months; then thefilter fabric was washed with water by a washing machine and dried(water washing treatment); the filter fabric was fibrillated into fiberswith a fiber length of 40 mm or shorter by a dry type automaticfibrillating apparatus manufactured by FUJI Corporation at a rotationspeed of 500 rpm (fibrillation treatment); dust was separated from thefibrillated fibers by Micron Separator (MS-1) manufactured by HOSOKAWAMICRON Corporation with a rotor rotation speed of 2100 rpm (powder dustseparation treatment); the fibers were lap-formed into a nonwoven fabricby a commercialized roller card (nonwoven treatment); further thenonwoven fabric was fixed with a base cloth having a strength of 750 N/5cm width and an elongation of 25% by needle punching (punchingtreatment); and finally the nonwoven fabric with the base cloth wasformed into a filter fabric with a thickness of 1.3 mm.

Comparative Example 1 New Filter Fabric

BF-800 manufactured by FUJI Corporation was used as a new filter fabricof Comparative Example 1.

Comparative Example 2 Regenerated Filter Fabric by Water Washing Method

As a filter fabric of Comparative Example 2 was used a filter fabricregenerated only by water washing treatment and not subjected to thefibrillation treatment, the powder dust separation treatment, thenonwoven treatment, the punching treatment, and the finishing treatmentas described above.

(Contents and Measurement Results of Comparative Tests)

According to Germany VDI 3926, the initial airflow degree, the finalairflow degree, and the outlet dust concentration were measured as thecomparative tests. The measurement conditions were as a filtration speedof 3.0 m/min. and an inlet dust concentration of 5.0 g/m³ and as dust,JIS 10 type (fly ash) was used. When the airflow degree reached 1000 Pa,backwashing by blowing compressed air was properly carried out and theoperation was continued for 8 hours for test duration.

The initial airflow degree means the airflow degree immediately afterstarting the test. The final airflow degree means the airflow degreeafter 8 hours test. The outlet dust concentration is the valuecalculated by dividing the total dust amount obtained at the outlet bythe operation for 8 hours by total air quantity blown during the 8 hoursoperation. The results are shown in Table 1.

TABLE 1 Example 1 (regenerated Comparative Comparative Example 2 filterfabric Example 1 (regenerated filter Measurement of the (new filterfabric obtained by value [unit] invention) fabric) water washing method)Initial 70 70 106 airflow degree [Pa] Final airflow 135 122 302 degree[Pa] Outlet dust 0.812 1.173 2.15 concentration [mg/m³]

According to the measurement results shown in Table 1, the regeneratedfilter fabric of Example 1 according to the invention had an initialairflow degree of 70 Pa, which is the same pressure loss as that of anew filter fabric (70 Pa). It implies that dust was removed to theextent approximately same to that of a new filter fabric and theregenerated filter fabric obtained is practically usable according tothe regenerating method of the invention. Also, much more dust wasremoved as compared with the result of the regenerated filter fabric(106 Pa) obtained only by water washing in Comparative Example.

The pressure loss after 8 hours use was 135 Pa, which was slightlynumerically high as compared with that (122 Pa) of the new filterfabric, however this value does not mean the regenerated filter fabrictends to be easily clogged in practically use, and the regeneratedfilter fabric have approximately same lifetime as that of the new filterfabric. As compared with the regenerated filter fabric of ComparativeExample (302 Pa), the clogging problem hardly occurs in the regeneratedfilter fabric of Example 1 of the present invention and it has a longlife as a regenerated filter fabric.

According to the measurement results shown in Table 1, the regeneratedfilter fabric of Example 1 had an outlet dust concentration of 0.812mg/m³, showing a higher dust collecting efficiency than not only that(2.15 mg/m³) of Comparative Example but also that (1.173 mg/m³) of thenew filter fabric. It is supposed to be because the fibers arefibrillated by the fibrillation treatment as shown in FIG. 2.

The filter fabric regeneration method and the regenerated filter fabricof the invention are applicable, for example, for a filtration type dustcollection apparatus in waste incineration facilities. Additionally,they can be applicable to various kinds of filtration dust collection ina crusher, a classifier, a drier, a coating booth, an asphalt plant, abuilding, and various kinds of furnaces as well as for pneumatictransportation and powder production.

1. A regeneration method of regenerating a filter fabric comprising atleast the steps of: fibrillating a used filter fabric; and producing anonwoven fabric from fibers obtained by the fibrillating.
 2. Theregeneration method according to claim 1 further comprising the step ofseparating powder dust adhering to the fibers obtained by thefibrillating prior to the producing of the nonwoven fabric.
 3. Theregeneration method according to claim 1 or 2, wherein the fibrillatingis effected by an automatic fibrillating apparatus.
 4. The regenerationmethod according to claim 1 or 2, wherein the used filter fabric is afilter fabric carrying a chemical agent for decomposing both dioxin andsubstances from which dioxin may be produced so as to prevent dioxinfrom adhering to the filter fabric while the filter fabric is beingused.
 5. The regeneration method according to claim 1 or 2, wherein theused filter fabric is mainly comprised of PTFE fibers.
 6. Theregeneration method according to claim 1 or 2, wherein the used filterfabric is comprised of at least PTFE fibers and inorganic fibers.
 7. Aregenerated filter fabric comprising at least a dust collection layerwhich is mainly comprised of fibrillated fibers obtained by fibrillatinga used filter fabric.
 8. The regenerated filter fabric according toclaim 7 further comprising a base cloth to which the dust collectionlayer is fixed.
 9. The regenerated filter fabric according to claim 7 or8, wherein the dust collection layer is comprised of the fibrillatedfibers mixed with auxiliary fibers.
 10. The regenerated filter fabricaccording to claim 7 or 8, wherein the dust collection layer comprises anonwoven fabric comprised of the fibrillated fibers.
 11. The regeneratedfilter fabric according to claim 7 or 8, wherein the used filter fabricis mainly comprised of PTFE fibers.
 12. The regenerated filter fabricaccording to claim 7 or 8, wherein the used filter fabric is comprisedof at least PTFE fibers and inorganic fibers.